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VH 21 May

 
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon May 21, 2007 11:05 pm    Post subject: VH 21 May Reply with quote

Just when I thought I was getting reasonably competent... I can't seem to find a way past this point. The puzzle looks like it there is a lot more "cleaning up" to do and I fear that I have missed something really obvious. Please help (and be gentle!).

Code:

+-------------+-----------------+------------+
| 1   4   9   | 256   3   256   | 8  256  7  |
| 256 8   3   | 2569  249 7     | 1  2456 29 |
| 7   25  26  | 1     8   24569 | 69 456  3  |
+-------------+-----------------+------------+
| 8   1   7   | 4     6   3     | 2  9    5  |
| 249 6   24  | 58    29  58    | 3  7    1  |
| 29  3   5   | 29    7   1     | 4  8    6  |
+-------------+-----------------+------------+
| 26  279 1   | 26789 5   2689  | 69 3    4  |
| 456 59  8   | 3     1   469   | 7  26   29 |
| 3   279 246 | 2679  249 2469  | 5  1    8  |
+-------------+-----------------+------------+


Many thanks.
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Mon May 21, 2007 11:11 pm    Post subject: Reply with quote

This is almost certainly a maverick solution but here we go

Code:

+---------+-------+-------+
| 1   4 9 | . 3 . | 8 . 7 |
| 256 8 3 | . . 7 | 1 . . |
| 7   . . | 1 8 . | . . 3 |
+---------+-------+-------+
| 8   1 7 | 4 6 3 | 2 9 5 |
| 249 6 . | . . . | 3 7 1 |
| 29  3 5 | . 7 1 | 4 8 6 |
+---------+-------+-------+
| 269 . 1 | . 5 . | . 3 4 |
| .   . 8 | 3 1 . | 7 . . |
| 3   . . | . . . | 5 1 8 |
+---------+-------+-------+

Play this puzzle online at the Daily Sudoku site

Once again I differ from the "official route"

Looking at the 249, 29, and 269 (yes this should be 26!) in col 1, I noted that an "external" 6 would release the 4 in box4 and an "external" 4 the 6 in box 7 BUT the 6 in Box1 would release the 4 in box2 creating a pair of 46s bearing down impossibly on box 7 hence r2c1 cannot be 6.

More formally-
If r2c1 is 6 then r5c1 is 4 and "overstrained" r9c3 has to be both 4 and 6
so r2c1 cannot be 6 r3c3=6..... and on to an easy solution
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Mon May 21, 2007 11:20 pm    Post subject: Reply with quote

Hint: Look for an XY-wing.

Code:
+-------------------+-------------------+-------------------+
| 1     4     9     | 256   3     256   | 8     256   7     |
| 256   8     3     | 2569  249   7     | 1     2456  29    |
| 7     25    26    | 1     8     24569 | 69    456   3     |
+-------------------+-------------------+-------------------+
| 8     1     7     | 4     6     3     | 2     9     5     |
| 249   6     24    | 58    29    58    | 3     7     1     |
| 29    3     5     | 29    7     1     | 4     8     6     |
+-------------------+-------------------+-------------------+
| 26    279   1     | 26789 5     2689  | 69    3     4     |
| 456   59    8     | 3     1     469   | 7     26    29    |
| 3     279   246   | 2679  249   2469  | 5     1     8     |
+-------------------+-------------------+-------------------+

n

n

n

n

n

n

n

n

n

Strong Hint: Look at one of the <69> cells.

Keith


Last edited by keith on Mon May 21, 2007 11:31 pm; edited 1 time in total
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon May 21, 2007 11:26 pm    Post subject: Reply with quote

Well I can see what you're saying, but I have no idea how I would go about finding such things!

Many thanks for your post George (and you're up very late in Dorset!). Is there a "method" to find this type of elimination, or do you just have a bizarre streak of logic?

Cheers
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Mon May 21, 2007 11:38 pm    Post subject: Reply with quote

Keith, thanks. Found it and solved it. I knew it would be something that I should have seen.

Cheers
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michelle.mcclure@gmail.co



Joined: 22 May 2007
Posts: 1

PostPosted: Tue May 22, 2007 12:33 am    Post subject: Reply with quote

Alas, I found at least two X-Y wings (or at least part of them), but didn't manage to get any farther than this:

+-------------------+-------------------+-------------------+
| 1 4 9 | 256 3 256 | 8 256 7 |
| 56 8 3 | 2569 249 7 | 1 2456 29 |
| 7 25 26 | 1 8 24569 | 69 456 3 |
+-------------------+-------------------+-------------------+
| 8 1 7 | 4 6 3 | 2 9 5 |
| 249 6 24 | 58 29 58 | 3 7 1 |
| 29 3 5 | 29 7 1 | 4 8 6 |
+-------------------+-------------------+-------------------+
| 26 79 1 | 26789 5 2689 | 69 3 4 |
| 456 59 8 | 3 1 469 | 7 26 29 |
| 3 279 246 | 2679 249 2469 | 5 1 8 |
+-------------------+-------------------+-------------------+

So, I"m missing the correct x-y wing, or I'm not seeing the obvious next step. Any additional hints most welcome!

Thanks,
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Tue May 22, 2007 1:38 am    Post subject: Reply with quote

Quote:
So, I"m missing the correct x-y wing, or I'm not seeing the obvious next step. Any additional hints most welcome!


Code:
+-------------------+-------------------+-------------------+
| 1     4     9      | 256   3     256   | 8     256   7     |
| 56    8     3      | 2569  249   7     | 1     2456  29    |
| 7     25    26     | 1     8     24569 | 69    456   3     |
+-------------------+-------------------+-------------------+
| 8     1     7      | 4     6     3     | 2     9     5     |
| 249   6     24     | 58    29    58    | 3     7     1     |
| 29    3     5      | 29    7     1     | 4     8     6     |
+-------------------+-------------------+-------------------+
| 26    79    1      | 26789 5     2689  | 69    3     4     |
| 456   59    8      | 3     1     469   | 7     26    29    |
| 3     279   246    | 2679  249   2469  | 5     1     8     |
+-------------------+-------------------+-------------------+


Take a look at the XY-Wing based in r2c1.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Tue May 22, 2007 11:49 am    Post subject: Reply with quote

George's logic seems to be an "if this is this - then that is that" solution. That's like guessing.
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Nwohio



Joined: 12 May 2007
Posts: 9

PostPosted: Tue May 22, 2007 7:45 pm    Post subject: Reply with quote

cgordon wrote:
George's logic seems to be an "if this is this - then that is that" solution. That's like guessing.


While I see where you are coming from, isn't "if this, this and if that, that" what so many of the conventional solving techniques rely on?
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Tue May 22, 2007 8:35 pm    Post subject: Reply with quote

I personally don't think so. Until recently, I'd get as far as I could with the "very hard" puzzles and then make a guess. Theoretically I could do this iteration right off the bat. Now I look for these XYZ or XY wing things or "skyscraper" patterns. Looking for these usually takes me longer than the guessing. But I feel I can now reach the solution without making an assumption. Perhaps it's a philosophical argument.
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Leon J. Taub



Joined: 22 May 2007
Posts: 2

PostPosted: Tue May 22, 2007 10:58 pm    Post subject: VH21May Reply with quote

Wouldn't the following analysis be a variant of a "unique rectangle" ?:

Note the "29s" in R6C1, R6C4 & R5C5. The 29 in R5C1 may therefore be removed, leaving only the 4. The puzzle solves easily from this point.
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Tue May 22, 2007 11:28 pm    Post subject: Re: VH21May Reply with quote

Leon J. Taub wrote:
Wouldn't the following analysis be a variant of a "unique rectangle" ?:

Note the "29s" in R6C1, R6C4 & R5C5. The 29 in R5C1 may therefore be removed, leaving only the 4. The puzzle solves easily from this point.


An UR has to be a rectangle and your one is not one. so the conclusion you reach may well be right but this is just chance!
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Tue May 22, 2007 11:31 pm    Post subject: Reply with quote

cgordon wrote:
I personally don't think so. Until recently, I'd get as far as I could with the "very hard" puzzles and then make a guess. Theoretically I could do this iteration right off the bat. Now I look for these XYZ or XY wing things or "skyscraper" patterns. Looking for these usually takes me longer than the guessing. But I feel I can now reach the solution without making an assumption. Perhaps it's a philosophical argument.


My attitude is - If I can see it without recourse to using a pencil then it is not trial and error.

As a matter of fact I saw this before recognizing the effect of the 9s in box7 (without which I couldn't see the XY wing!)
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Leon J. Taub



Joined: 22 May 2007
Posts: 2

PostPosted: Wed May 23, 2007 1:56 am    Post subject: VH21May Reply with quote

Thanks for your comment, George. I see now that the UR MUST be a rectangle!
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peter.s



Joined: 29 May 2007
Posts: 2
Location: Belgium

PostPosted: Tue May 29, 2007 7:49 pm    Post subject: Reply with quote

sorry Marty R. but I don't see it :
Take a look at the XY-Wing based in r2c1
please help !
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David



Joined: 02 Jun 2006
Posts: 58
Location: Bedford, UK

PostPosted: Tue May 29, 2007 8:09 pm    Post subject: Reply with quote

Peter S

If you look at r2c1 (56), r3c2 (25) and r7c1 (26) they form an XY wing and the two pincers can be used to eliminate the '2' in r9c2. This leaves you with a naked pair (79) in c2 which should help you considerably.
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peter.s



Joined: 29 May 2007
Posts: 2
Location: Belgium

PostPosted: Tue May 29, 2007 8:25 pm    Post subject: Reply with quote

David
Thanks , I did not see that the 2 of r9c2 was involved in the XY-wing !
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